Escalate privileges to test single user installation

tests/dockerfiles/debian9/Dockerfile

@@ -1,7 +1,5 @@
 FROM debian:9
 
-RUN useradd -ms /bin/bash user
-
 RUN apt-get update && \
     apt-get install -y \
 			curl \
@@ -11,4 +9,7 @@ RUN apt-get update && \
 			systemd \
 		&& rm -rf /var/lib/apt/lists/*
 
+RUN useradd -ms /bin/bash user \
+		&& echo 'user ALL=(ALL) NOPASSWD: ALL' >> /etc/sudoers
+
 CMD ["/bin/systemd"]